I don't have the L0D-CE, but i *do* have the older L0P-SE, and i have an Arc AAA-P on order (should be here tomorrow)
my L0P-SE has been a reliable light, nice smooth hotspot-to-spill transition, the three power levels are nicely implemented, however, the "Hard Anodizing" isn't wearing well, there are worn areas all over the light, and not just on the corners, which is a known weak spot for HA in general, the L0P-SE also uses PWM to dim the LED, and I do notice it, annoying but not a dealbreaker
the Arc, from what i've heard, is far more durable, has better Hard Anodizing, a grippiier knurling, and is reasonably bright for a 5MM based device, that said, it *IS* a 5MM LED, and has a slightly bluish beam, and has only one light level
Arc advantages;
Superior HA
durable, simple design
efficient, long runtime
one power level
Chemkoted interior to protect against battery corrosion and increase electrical conductivity
Arc disadvantages;
"Angry Blue" Nichia 5mm LED
exposed LED (recessed, but exposed)
one power level
L0D-CE advantages;
nice, clean white tint, smooth hotspot-to-spill transition
multiple power levels
glass window protects LED
L0D-CE disadvantages;
HA less durable than Arc
It basically comes down to what you're looking for, the Fenix L0 series lights can double both as a keychain light, *AND* a primary light, and if you want a decent general-purpose light are a great little light, however, the multiple power levels/modes can complicate the user interface, and some people notice PWM flickering more than others, the Fenix Hard Anodizing seems marginally less durable than SureFire/Arc/HDS/etc... but let's be honest here, HA wear is a *COSMETIC* issue only, it does not affect the functionality of the light
the Arc AAA is a great backup light, a light that you can depend on to be utterly reliable, no it's not as bright as the Fenix, but it's far more durable, reliable, and thanks to the efficiency of the 5MM LED, more battery efficient
I went with the Arc simply because I already carry much brighter lights (E1L-SR and Aviatrixed A2 Aviator, Inova X5 White LED), and I want an absolutely bulletproof, reliable backup light, runtime and durability are priorities here
It all depends on what *you* want